Crystalline boric oxide



after.

Patented Jan. 9, 1940'.

, Westinghouse Electric & Manufacturing Cjompany, East Pittsburgh-Ta a corporation of Application July 20, 1938; Serial No. 220,177 I ,1 f4 Claims. (01. 23-149) Y This invention relates tocrystalline boric'oxide This application is acontinuation-in-part of copending application, Serial No. 1 56,829, filed July 31, 1937, and directed toa Method'of producing: crystalline boric oxide-new issued as Patent 2;113"],lili58' and which is assigned to the same assignee as this invention 1 An: object of this invention isto'provide as a new product, crystalline boric oxide Another object of this invention i acrystalline boric oxide which has a high melt ing'point an'd'a highdensity;

Other objects of this invention W111 become apparent from the following description and the i6 boric oxide of this invention. I

In accordance with invention will In producing this invention, *boricacid may-be employed. 0 The boric acid employed maybe of-any-of the'types or technical grades having a moderate purity which' can be. purchased in'the open market. These technical grades ofithe boric acid' are tobe preferred forthe formation of" the first-.-seed crystals since it has beenfound through experiments that the growing ofthe crystalsmaybe accomplished at a faster" rate withrthe. moderately pure boric acidthan where chemically pure boric acidis employed. 1

Inv order to induce an 1n1t1al crystallization, the crystals of which*may be employed :for the purpose of seeding other, liquids, as' sdescribed hereinafter, a quantity of the "moderately pure I boric acid'maybe placed inla suitable container, not shown, which is open to the atmosphere through a small 'ventand then subjected to a melting point of boric acid to fuse it until it becomes a viscous liquid. Theheating of theiboric j acid in the container may. be byany v suitable means, although it is preferredthat the heating be accomplished in an electric furnace'provided with an automatic temperature controlfor con"- trolling the heatingtemperature'.

, Theheatingmay be continued until all-jof the excess steam escapes to the atmosphere and-an examination of the'viscous liquidreveals that the s to; provide accompanying drawing, the single figure of which illustrates the solubility curveof the crystalline this g invention, an anhydrous crystalline boric oxide is provided. The

. crystalline boricoxide is a newproduct'having a high density of 2.42 and a high melting point of between about 460 and 470 C.' Z'Other. chare acteristics of the crystalline borio oxide" of this be described more fully herein-- the crystalline boric oxide-of substantially constant temperature alcovev the fused boric acid retains water in solution in" an amount ranging from 8% to 14% by weight. It-

has been found necessary-to havewater in' solution in the fused boric acid within the ranges given in order that 'crystallization ot the liquid may be obtained. This isthe percentageof-water that remains in boricacid-whenfused at atmos- "pheric pressure within the temperature range If higher, temperatures were: em- -,ployed, it would be necessary also to go to pres- 2 sures higher than atmospheric pressure;

employed.

With the content of thefwater in solution rang shapetofabout .3 millimeter indiameter. Contin- I I ued'application ofthe'substantially constant temper'ature'to the, viscous liquid. causes the initial minute crystalline bodiesto multiply with the lib eration of Water vapor until the whole of the liquid in the container becomes solidified; If the viscou'sliquid is examined when only 1%: remains uncrystallized, itwill be found that the 1,%,of

the liquid still has a content 'of waterfin solution.

in the boric. acid ranging from 8% to 14% by weight indicating that thiscontent'is necessary in order that the crystallization may be" com-- pleted. As an example of thepspeed at'which the viscous liquid crystallizes, a liter of the boric acid;

of moderate purity completely crystallized in a period of 7 days when heat treated as'descri-bed hereinbeforewhereas a: literof b'oric" acid of chemical purity requiredtwice as :long a-time.

In heatingthe viscous liquid to induce-theime tial crystallization and cause the liquid to completely crystallize, it is necessary that thetemperature of the heating be 'below'the'tem'perature at which the crystalswill dissolve and also to maintain the'content of water "in solution with the fused bori c acidiwithin the ranges "given hereinbe fore.v A particularly efiective. ,heating range has been found to be between 220. C. and

' In order to producethe crystallinejboric oxide in quantity, the crystals formed by the initial crystallization described 'hereinbefo're may be em:

played as seeds forinitiating the crystallization in a similar manner to that described in pro- After being ducing the initial crystallization. fused under atmospheric pressureat a temperature above the melting point of boric acid and brought to a temperature of between 225 C. and 250 C., the seeds obtained from the initial crystallization may be introduced into the viscous] liquid.

The crystalline boric oxide seeds added to the Viscous liquid may be many desired amount, al-

though it is found that crystalline boric oxide seeds of the order of 1% to 1% by weight of the liquid to be crystallized are sufficient to cause a rapid crystallization of the viscous liquid. If a larger quantity of the initial crystals or seeds of boric oxide is added to the viscous liquid the crystallization action .Will be carried to completion in a shorter period of time.

An examination of the viscous liquid during the crystallization transformation reveals that at first a cloudiness is formed in the clear fused boric acid which increases with the escape of steam as bubbles therefrom, until the liquid becomes more and more pasty and finally solid. The crystals obtained are of microscopic size, the resulting crystalline mass being an anhydrous, white, opaque, non-glass like, stony solid and strong produce which is somewhat resilient under blows from a hammer. The crystalline structure of the new oxide can be definitely established by the sharp lines of its X-ray pattern.

Referring to the drawing, the solubility curve of the crystalline boric oxide of this invention is illustrated as-added to the diagram of M. Von

Stackelber'g, F. Quatram-and Jutta Dressel, Z. Elektrochem., 43, 14-28, (1937). In the graph, the ordinate is given as temperature in degrees C.

and the abscissa as B2O3% by weight. The solu-' B 2 O a in the liquid Percent :solubilities may be easily determined by enclosing 25 g. of the crystalline oxide with small amounts of boric acid in sealed tubes of Pyrex glass and keeping them in electric ovens at the temperatures given until equilibrium of the liquid and the solid is obtained. A portion of the liquid may then be drained from the solid and solidified by rapidly cooling after which it may be analyzed by hydrating it under Water to HaBOs, then drying the acid at 35 C. and

Weighing and calculating the BzOscontent by use of the factor 0.5631. This method of analyzing the crystalline oxide is quite accurate and is believed to be better than 99.6%.

The crystalline boric oxide of this invention is found to have a density of 2.42 as determined by weighing it in transformer oil after the removal of air in vacuum and to have a high melting point of between 460 C. and 470 G.

Since the crystalline boric oxide is free of water and,therefore, non-volatile, it is particularly useful in certain branches of industrial chemistry and in particular glass making. Other uses of the crystalline boric oxide of this invention are as reagents in analytical chemistry or as fluxes for use in welding as in metallurgy. The crystalline boric oxide of this invention may also be employed in the production of elemental boron.

and boron alloys by reduction with magnesium or otheractive metals. A further use of the crystalline boric oxide of this invention is as a desiccating agent, since it can take up about 77% of its Weight of water in going backv to boric acid.

Although the production ofthe new, product, crystalline boric oxide, has been. described with reference to a particular method forproducing it, the new product of this invention is not to be limited thereto for it is conceivable-that other methods may be developed for producing the crystallinelhoric oxide. This invention is, therefore,not to be limited except insofar as is necesp nded c aimsv a j I I claim as my invention: l

1. As a new product, crystalline boric oxide having the formula B203 and a density of about 2.42. A

2. As a new product, crystalline boric oxide having. a melting point of between aboutv 460 and 470C. and a density of about 2.42.

,3. As a new product, crystalline boric oxide, the crystalline boric oxide being substantially anhydrous, white, and opaque andhaving a, den-. sity, of about 2.42. 1

4. As a new product, boric oxide in a crystalsitated by the priorart and the scope of the apline form, the, crystals being of microscopicsize, thecrystalline boricoxide having-a melting point LEON lVIoCULLOCI-I. 

